In order to cool their hot parts, in particular the combustor and the turbine through which the hot gas flows, existing gas turbines (gas turbine systems) use either cooling media taken from the compressor at a suitable pressure, and which sometimes are further cooled, and which, after they have been used to cool the hot parts, are added to the turbine stream. Such a method and such a gas turbine system are known, for example, from publication U.S. Pat. No. 5,611,197. These existing gas turbines use closed cooling circuits supplied from an external cooling medium source, in most cases water or steam. In the latter case, frequently found in combination power plants, the cooling heat often can be used in the process that follows. Another possibility, described, for example, in EP-A2-0 899 425 of the applicant, combines, especially in the case of blade cooling, a closed steam cooling system in the main part of the blade with an open cooling system in the area of the leading blade edge.
The first category has the disadvantage that the cooling medium, which inherently bypasses heating in the combustor, in most cases undergoes a higher pressure loss in the cooling section than is necessary for the cooling task. In addition, mixing losses are created when the cooling medium enters the main stream. Both represent significant process losses that have an important adverse effect on the efficiency of the process overall.
The second category of externally supplied cooling systems and, in particular, also the third category of the combined cooling systems, does not have these disadvantages or is only affected by them to a limited degree; however, their operation becomes dependent on an external coolant supply, which is associated with an increased level of complexity as well as increased cost and safety risks.
The initially mentioned U.S. Pat. No. 5,611,197 discloses a gas turbine with a closed cooling system for the guide and rotating blades and the hot gas housing of the turbine, in which air with a specific pressure is removed from the compressor at an intermediate pressure level or at the outlet, this air is supplied as cooling air through the components to be cooled, and is then again fed into the compressor at a suitable, lower pressure level. Prior to being fed into the compressor, the returned cooling air hereby also can be additionally cooled inside a cooler.
This known type of closed cooling circuit has significant advantages in terms of simplicity of design and operation and influence on the overall efficiency when compared to the types of cooling described previously in this document. The disadvantage, however, is that, especially with respect to the turbine blades, a film cooling of the component surfaces exposed to the hot gas is not easily possible with this hermetically sealed cooling circuit. This means that a film cooling either must be eliminated—which reduces the load bearing capacity of the components and, as a result, the efficiency; or a separate cooling circuit, which again would increase the complexity of the system and thus its susceptibility to trouble, must be provided for the film cooling.